Field of the Invention
The present invention relates to a polymer nanofiber accumulated body and a method of producing the same.
Description of the Related Art
In recent years, a polymer nanofiber accumulated body, which is formed as described below and typified by a polymer nanofiber sheet, has been attracting attention. A plurality of polymer nanofibers each containing a polymer material are accumulated, and the polymer nanofibers are three-dimensionally entangled with each other to form the accumulated body.
Incidentally, in a related-art polymer nanofiber accumulated body, polymer nanofibers have been three-dimensionally entangled with each other. However, the entanglement is based on only physical entanglement, and hence the related-art polymer nanofiber accumulated body tends to have a low mechanical strength and to be weak against a tensile force or friction. Accordingly, the accumulated body has involved problems in terms of practical use. In view of the foregoing, an approach for an improvement in mechanical strength of a polymer nanofiber accumulated body has been developed.
In Japanese Patent Application Laid-Open No. 2011-214170, there is a disclosure of an approach involving performing a partial bonding treatment in which a plurality of polymer nanofibers are partially bonded to each other by heating a thread-like polymer nanofiber structural body formed by twisting the polymer nanofibers. In addition, in Japanese Patent Application Laid-Open No. 2011-214170, there is a disclosure that the thread-like structural body (polymer nanofiber accumulated body) formed of the polymer nanofibers is improved in strength by the approach.
However, in the approach of Japanese Patent Application Laid-Open No. 2011-214170, it is difficult to control treatment conditions, such as a temperature, such that the conditions may be suitable for the performance of the partial bonding treatment of the polymer nanofibers. Accordingly, the bonding between the polymer nanofibers does not progress or the polymer nanofibers are largely melted depending on their surrounding environment. When the bonding between the polymer nanofibers does not progress, a strength required for the polymer nanofiber structural body is not obtained. Meanwhile, when the polymer nanofibers are largely melted, the following problem occurs. Surrounding polymer nanofibers are completely integrated with each other, and hence the diameter of a fiber itself becomes several micrometers or more.